1. Field of the Invention
The present invention relates to a reflective plate used in a reflective type liquid crystal display, a method of making same, and the reflective type liquid crystal display.
2. Description of the Related Art
In recent years, demands have been built up for down-sizing, reduced power consumption and cost down of a device equipped with a liquid crystal display, such as a personal computer, a television set, a digital video camera, a digital camera and the like. In order to meet such demands, development has been progressed of a reflective type liquid crystal display using reflection of incident light from outside instead of a back light for illumination of a liquid crystal panel.
FIG. 1 shows a schematic sectional view of a structure of a conventional reflective type liquid crystal display. A liquid crystal display 1 includes an insulated substrate 2, an uneven layer 16, a reflective film 11, a leveling layer 17, a TFT 8, a pixel electrode 18, a liquid crystal layer 12, a transparent common electrode 19, a color filter 14 and a transparent insulated substrate 15. Furthermore, the TFT 8 is formed of a source electrode 6, a drain electrode 7, a semiconductor layer 5, a gate insulated film 4 and a gate electrode 3.
The uneven layer 16 can be formed with ease by embossing, in which irregular surface is shaped by pressing a die having a reverse pattern thereon. More specifically, as shown in FIG. 2A, resin 16a such as acrylic resin is coated on the insulated substrate 2 and a metal die 20 having irregular surface thereon is pressed onto the resin 16a at a temperature of not less than a glass transition point to less than a melting point (FIG. 2B) Thereafter, the resin 16a is hardened, followed by removal of the metal die 20 to complete the uneven layer 16 shown in FIG. 2C. A reflective film 11 is formed by vacuum evaporating a high reflective metal thin film that is for example aluminum onto a surface of the uneven layer (FIG. 2D).
The leveling layer 17 can be formed on an upper surface of the reflective film 11 by spin coating, for example, a polyimide resin (FIG. 2E).
On the other hand, in the reflective type liquid crystal display as described above, it is important how efficiently to use peripheral light in order to raise a luminance on a liquid crystal screen. Hence, as shown in FIG. 3, a method has been tried with which light-collecting performance of reflective light is enhanced, by that a slope of a convex formed on the uneven layer 16 becomes steeper from the center on the reflective plate toward the outer periphery and, simultaneously, a height of the convex is also increased in the same direction, while a global shape of the reflective surface is formed like a parabolic line.
If the uneven layer 16 having this shape is, as shown FIG. 4A, tried to be shaped by embossing, the metal die 20 could not be pressed into the uneven layer 16 deeper when shallow recesses formed in the central area of the metal die 20 is filled with the resin to the full. Therefore, a wrong shape is, as shown in FIG. 4C, formed on the surface of the uneven layer 16. It is understood that, as a result, the uneven layer 16 having the shape as shown in FIG. 3 cannot be formed with good precision by embossing.
Even if the reflective surface with the shape shown in FIG. 3 was able to be formed in a different method, the leveling layer 17 formed on the reflective film 11 with a spin coating method would inevitably depress at the central area below the peripheral area thereof as shown in FIG. 5A. If the TFT 8, liquid crystal layer 12, transparent insulated substrate 15 and the like, as shown in FIG. 5B, are formed in this state, a cell gap in the central area of the transparent insulated substrate 15 is different from one in the peripheral area thereof. Therefore, an interference condition alters according to a position on the transparent substrate 15, which causes a mottled pattern to thereby drastically degrade a display quality of a liquid crystal display.